A DNA match —a crime "solved" by the FBI's CODIS database— does not mean that an arrest was made, that a criminal was prosecuted, or even that detectives considered a case closed. So how many DNA matches lead to an arrest and how often is the ball dropped? Unknown, no government agency keeps track.

But a USA TODAY investigation found almost three dozen cases during the past five years in which investigators failed to pursue potential suspects whose DNA matched evidence found at crime scenes. DNA matches that could have closed cases weren't pursued because of basic police foul-ups, such as overlooking a telephone message reporting the match. According to USA TODAY, backlogs of unsolved "cold cases" that threaten to overwhelm some big-city police departments caused matches to be ignored. In some jurisdictions — Richmond, Va., Cincinnati, and DeKalb County, Ga. — police offered no explanations for why matches were not pursued.

Among the cases USA TODAY found:

•In Oakland, in June 2004, the DNA of convicted child molester Kalonji Lee matched DNA from an attempted sexual assault of a 10-year-old Oakland girl the previous January. Police did not contact Lee until after he had molested another Oakland 10-year-old in December 2004, deputy chief Howard Jordan confirms. Lee was caught for the second assault after the victim's parents spotted his picture on California's "Megan's Law" website and alerted detectives.

•In Cincinnati, September 2004, the DNA of career felon Gary Box matched DNA left at a December 2001 rape and abduction that Cincinnati police had been unable to solve. At the time of the match, Box was serving a prison sentence for assault. But police did not contact him until May 2005, after he had been released from prison and had returned to Cincinnati. Court files show that police acted after being alerted by Box's victim, who encountered him by chance while walking in a local park.

•In Georgia, March 2003, the DNA of convicted burglar and sex offender Floyd "Tony" Arnold matched DNA left at separate rapes in Fulton and DeKalb Counties. The rapes had taken place in 1993 and 1995. But neither Fulton nor DeKalb authorities contacted Arnold, according to both police departments, even though at the time of the matches he was in Georgia's prison system serving a five-year sentence for cruelty to children. The unpursued matches came to light last December, when Arnold was matched through a third DNA hit to a 1981 Cobb County rape for which another man had been wrongly convicted. That man, Robert Clark, Jr., had served almost 24 years in prison.

•In Oregon, 2002, the state police crime lab used DNA to match 26 men to unsolved Portland burglaries. The names were reported to Portland police, department spokesman Detective Paul Dolbey acknowledges. None was followed until one of the 26 suspects was matched again to an additional burglary, and lab technicians pointed out the earlier matches.